Separation of contaminants from polyester materials

ABSTRACT

The present invention is generally directed to a process for separating and recovering post-consumer polyester from various contaminant materials. The invention can be utilized to separate post-consumer polyester from various contaminants including glass, dirt, paper, metal, glue, dye, and the like. The disclosed process includes several stages including a preparation stage, in which a portion of the contaminants can be removed from the polyester, as well as a reaction stage, in which a portion of the polyester can be saponified and contaminants can be physically separated from the polyester. In addition, during the reaction stage, certain hard-to-separate contaminants, such as aluminum and polyvinyl chloride, can react to a form more easily separable from the polyester.

BACKGROUND OF THE INVENTION

Polyesters are polymeric materials made from the esterification ofpolybasic organic acids with polyhydric acids. Perhaps the most commonlymade and used polyester is polyethylene terephthalate (PET), which canbe manufactured by reacting terephthalic acid with ethylene glycol.

Polyesters are currently being used in increasing amounts in variousapplications. For instance, polyesters are commonly used to make manytypes of beverage and food containers, photographic films, X-ray films,magnetic recording tapes, electrical insulation, surgical aids such assynthetic arteries, fabrics and other textile products.

Because polyesters can be remelted and reformed, ongoing efforts areunderway to efficiently recycle as much polyester as possible after use.Before polyester can be recycled, however, it is necessary to separatethe post-consumer polyester from contaminants, i.e., materials that maybe found mixed with or attached to the polyester. For instance,contaminants can be loose and mixed with the polyester materials, can beattached to the surface of the polyester materials, as with labelsattached to the surface of the materials, or can be within the polyestermaterials, as in the case of embedded or entrained materials.

What is needed in the art are improved methods for removing contaminantsfrom polyester materials, and in particular, from post-consumerpolyester materials.

SUMMARY OF THE INVENTION

In general, the disclosed invention is directed to methods forseparating contaminants from polyester. In particular, the disclosedprocess can separate polyester from contaminants that are embedded orentrained in the polyester, contaminants that are attached to thesurface of the polyester, and/or contaminants that are merely mixed withthe polyester.

The method can be described as a multi-stage process including apreparation stage and a reaction stage. If desired, the preparationstage can include an operation for chopping the polyester and forming amixture including polyester and contaminants. For instance, in oneembodiment, the polyester can be chopped to a flake size of less thanabout 15 mm.

The preparation stage can include various operations for physicallyremoving a portion of the contaminants from the polyester mixtureincluding, for instance one or more elutriation processes, in whichvarious loose contaminants, including contaminants such as metals andpaper, can be removed from the mixture or a dry-cleaning operation, inwhich contaminants can be removed from the substantially dry mixture byfluidizing the dry mixture and spinning the dry mixture about the axisof the cleaning chamber such that a portion of the mixture collides witha mesh wall as the mixture spins about the axis, and passing a portionof the contaminants through the mesh. Another dry separation processthat can be included in the preparation stage is a color-sortingprocess. A color sorting process during the preparation stage can removevarious contaminants including, for example, metals and colored PET,such as TiO₂-containing PET.

In one embodiment, the mixture can be subjected to a high quality metaldetection and removal operation. According to this particularembodiment, multiple metal detectors can be placed in series and/orparallel combination to form banks of metal detectors. The mixture canthen be fed through one or more banks of metal detectors for the removalof metal contaminants. At each metal detector in the bank, the streamcan be split into accepted materials (those that pass on to the nextstep in the process) and rejected materials (those containing metal). Inone embodiment, materials can be recycled back through the metal removaloperation. In those embodiments wherein two or more individual metaldetectors are arranged in a series combination, the sensitivity of themetal detectors in series can be increased with progression of theseries. A high quality metal detection and removal operation can notonly increase the amount of metal removed from the product stream ascompared to previously known processes, but can also, with the additionof the recycle stream, reduce the amount of polyester that can be lostfrom the stream during the separation process.

In addition to the separation operations generally carried out when themixture is dry, the preparation stage of the process can include one ormore aqueous separation operations. For example, one or more aqueousseparation operations such as high intensity washing operations andsink/float operations can be utilized. In one embodiment, the processcan be further improved by recirculating the water used in the aqueousseparation operations through a recirculation tank.

Following the preparation stage, the mixture can be processed accordingto a reaction stage that can include a high energy mixing operation aswell as a heat setting operation. During the high energy mixingoperation, a slurry including the polyester/contaminant mixture and analkaline composition can be formed within or optionally prior to beingfed into a high-energy mixer. For example, the alkaline composition caninclude sodium hydroxide, calcium hydroxide, magnesium hydroxide,potassium hydroxide, lithium hydroxide, or mixtures thereof. The amountof alkaline composition added to the slurry can include an amount ofalkaline so as to react with less than all of the polyester. Forexample, the alkaline composition that can be combined with the mixturein one embodiment can be an amount sufficient to react with less thanabout 20% by weight of the polyester.

If desired, the slurry can be formed in a more conventional mixer priorto being fed to the high-energy mixer for reaction. For example, thealkaline composition and the dry polyester mixture can first be combinedin a low-energy mixer prior to being fed to the high-energy mixer.During the low-energy mixing, the polyester flakes contained in theslurry can be coated with the alkaline composition. In addition, in oneembodiment, the energy input to the slurry while contained in thelow-energy mixer can be controlled such that the alkaline compositioncan react with certain impurities that may be included in the polyestermixture. For example, the low-energy mixer can be maintained so as topromote the reaction of aluminum contaminants with the alkalinecomposition while the slurry is in the low-energy mixer.

The high-energy mixer used can be a mixer in which sufficient energy canbe imparted to the slurry from the mixing action itself so as to promotea saponification reaction between a portion of the polyester and thealkaline composition. In particular, during the high energy mixingoperation any heat added to the high-energy mixer will not independentlyprovide sufficient energy to promote the saponification reaction.

Following the high energy mixing operation, the mixture can be furtherprocessed, for example, in those embodiments wherein food-gradepolyester materials are desired for the polyester product of theprocess. In one embodiment, following saponification in the high-energymixer, the slurry can be heated to a temperature that is not greaterthan the melting point of the polyester. In particular, the mixture canbe heated in an environment including less than about 80 ppm watercontent. Optionally, the mixture can be heated in an oxygen-starvedenvironment. This is not a requirement of the invention, however, and inother embodiments, the mixture can be heating in an oxygen-richenvironment.

If desired, the mixture can be pre-heated prior to the heating step, forinstance to dry the mixture. According to this embodiment, the mixturecan be pre-heated to a temperature less than about 160° C.

The method can also include operations for recovery of variousby-products produced during the separation and/or reaction operations.For example, in one embodiment, ethylene glycol can be produced in thesaponification reaction. If desired, the ethylene glycol can berecovered following the saponification reaction. Another by-product ofthe process that can be produced and recovered, if desired, is theterephthalic salt that can also be produced in the saponificationreaction.

The method can beneficially be utilized to remove many hard-to-separatecontaminants from polyester. For instance, in one embodiment in whichthe contaminants include polyvinyl chloride, a portion of the alkalinecomposition can react with the polyvinyl chloride, causing the polyvinylchloride to become dechlorinated during the reaction.

Another contaminant that has proven difficult to separate frompost-consumer polyester in the past has been aluminum. According to oneembodiment of the present invention, aluminum mixed with the polyestercan react with a portion of the alkaline composition and be removed fromthe mixture, for instance as an aluminum salt or as the brittle aluminumremains of the reaction.

BRIEF DESCRIPTION OF THE FIGURES

A full and enabling disclosure of the present invention, including thebest mode thereof, to one of ordinary skill in the art, is set forthmore particularly in the remainder of the specification, includingreference to the accompanying figures including:

FIG. 1 illustrating a flow diagram of one embodiment of a polyesterrecycling process according to the present invention; and

FIG. 2 illustrating a flow diagram of one embodiment of a multi-step,high quality metal removal system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to various embodiments of theinvention. Each example is provided by way of explanation of theinvention, not limitation of the invention. In fact, it will be apparentto those skilled in the art that various modifications and variationscan be made in the present invention without departing from the scope orspirit of the invention. For instance, features illustrated or describedas part of one embodiment, can be used on another embodiment to yield astill further embodiment. Thus, it is intended that the presentinvention cover such modifications and variations as come within thescope of the appended claims and their equivalents.

The present invention is generally directed to a process for separatingand recovering post-consumer polyester from various contaminantmaterials. The invention can be utilized to separate post-consumerpolyester from various contaminants including glass, dirt, paper, metal,glue, dye, and the like. Beneficially, the disclosed process includesmultiple stages, including a preparation stage, in which the a portionof the contaminants can be removed from a mixture containingcontaminants and polyester, as well as a reaction stage, in which aportion of the polyester can be saponified thus allowing additionalcontaminants to be separated from the polyester. In particular, duringthe reaction stage of the process, contaminants that are physicallyattached to or within the polyester can become detached, so as to bemore easily removed from the mixture in separation steps. In addition,during the reaction stage of the process, certain hard-to-separatecontaminants, such as aluminum and/or polyvinyl chloride (PVC) can reactto a form more easily separable from the polyester. In certainembodiments, the disclosed process can significantly reduce the totalproduction of wastewater as well as the level of contamination ofwastewater in a polyester recycling process.

In general, a polyester is defined as an esterification or reactionproduct between a polybasic organic acid and a polyol. It is believedthat any known polyester or copolyester may be used in the process ofthe present invention. However, in one particular embodiment, theprocess of the present invention is directed to a class of polyestersreferred to herein as polyol polyterephthalates, in which terephthalicacid serves as the polybasic organic acid.

As used herein, a polybasic organic acid refers to any organic acidhaving two or more carboxyl groups (—COOH). Most polyesters are derivedfrom dibasic acids, also referred to as dicarboxylic acids. Polybasicacids can have a linear or a cyclic conformation. Examples of linearpolybasic acids that can be used to make polyesters include thealiphatic dicarboxylic acids. In particular, the aliphatic dicarboxylicacids having up to ten carbon atoms in their chains can be used. Theseacids include adipic acid, glutaric acid, succinic acid, malonic acid,oxalic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,maleic acid, and fumaric acid.

Cyclic polybasic organic acids, on the other hand, include thecarbocyclic dicarboxylic acids. These acids include phthalic acid,isophthalic acid, and terephthalic acid. In particular, terephthalicacid is used to make polyethylene terephthalate, which is perhaps themost common commercially available polyester.

As described above, a polybasic organic acid can be reacted with apolyol to produce a polyester. Polyols are compounds that contain atleast two hydroxyl groups. Many polyesters are synthesized with a diol.Diols are normally prepared from an alkene by the net addition of twohydroxy groups to the double carbon bond in a method known ashydroxylation. Polyols are commonly referred to as glycols andpolyhydric alcohols. Examples of polyols used to make polyesters includeethylene glycol, propylene glycol, butylene glycol, and cyclohexanedimethanol.

For exemplary purposes, Table 1 contains a nonexhaustive list ofcommercially available polyesters that may be recovered and recycledaccording to the present invention. For each polyester, thecorresponding polybasic organic acid and polyol are provided. TABLE 1POLYBASIC ORGANIC POLYESTER ACID DIOL Polyethylene Terephthalic AcidEthylene Glycol Terephthalate Polybutylene Terephthalic Acid ButyleneGlycol Terephthalate PETG Co-polyester Terephthalic AcidCyclohexane-dimethanol And Ethylene Glycol PBTG Co-polyesterTerephthalic Acid Cyclohexane-dimethanol And Butylene GlycolPolycyclohexane- Terephthalic Acid Cyclohexane-dimethanol dimethanolTerephthalate PEN Polyester Naphthalene Ethylene Glycol DicarboxylicAcid

In one particular embodiment of the disclosed invention, the polyesterbeing recovered can be polyethylene terephthalate (PET). Accordingly,much of this discussion is directed to PET, though this should not beconsidered as limiting the invention in any way to the recovery anddecontamination of PET.

In one embodiment, the process of the present invention can beconsidered as a three-stage operation for removing contaminants frompolyester and can include a preparation stage, a reaction stage, and afinishing stage. In addition, each stage of the overall process caninclude one or more individual operations. In one embodiment, thepreparation stage can include at least one dry separation operation andat least one aqueous separation operation, during which contaminants canbe removed from the polyester-containing mixture. Following thepreparation stage can be a reaction stage in which the mixturecontaining polyester and contaminants can be combined with an alkalinecomposition. The alkaline can react with a portion of the polyester in asaponification reaction as well as reacting with various possiblecontaminants in the mixture so as to degrade or otherwise chemicallyconvert the contaminants to a form more easily separable from polyester.This stage of the process can also include the separation and removal ofcontaminants from the mixture, if desired. The reaction stage can alsoinclude various heat setting reactions that can, among other benefits,further purify the polyester substrate and improve the physicalcharacteristics of the product material. The final finishing stage ofthe process can include operations to improve the quality of the productthrough, for example, washing and sorting of the product as well asadditional separation operations.

The process of the present invention can run continuously or can be setup as a batch system. In addition, any particular operation of theprocess can be run as a continuous or batch system. Practically anymaterial containing a polyester can be processed according to theinvention. In one preferred embodiment, the polyester materials can berecovered from the solid waste stream, thus alleviating manyenvironmental concerns and disposal problems. In one particularembodiment, the process can be directed to recovery and recycling offood and/or beverage containers made from PET. Through the process ofthe present invention, polyesters can be separated, recovered and reusedfrom post-consumer waste, even when the polyesters are found mixed withcertain hard-to-separate materials, such as polyvinyl chloride oraluminum, adhered to various coatings, or entrained with either variousmaterials, such as organic and/or inorganic compounds. Unfortunately,many post-consumer polyesters are currently being disposed of inlandfills or are being incinerated after use due to a lack of aneconomical process that can be used to separate and recover thepolyester.

Included among the contaminants that can be adhered to or containedwithin the feed polyester materials that the disclosed process canbeneficially remove are various barrier materials. Barrier materialsremovable according to the present invention can include barriercoatings that can be, for example, applied to beverage containers inorder to prevent carbon dioxide and/or oxygen flow across the substrate.Other barrier materials that can be removed according to the presentprocess can include certain chemical barrier material additives, forexample chemical scavenger materials added to the polyester materialsduring initial formation, and/or the breakdown products formed uponreaction of such additives. In one embodiment, the disclosed process canbe utilized to remove barrier materials applied as coatings for locationbetween layers on multi-layer bottles.

In addition to coated barrier materials, the process can remove othercoatings from the polyester materials as well. For instance, the processcan remove applied labels, including paper and/or polymeric labels,screen-printed labels, and the like. The term “screen printed labels”generally refers to inks that have been directly applied to polyestercontainers, such as beverage containers. For instance, many soft drinkcontainers are typically labeled with an epoxy-based ink. In the past,many problems have been encountered in attempting to separate polyesterfrom these types of coatings and inks.

A non-limiting exemplary list of barrier materials (both coatings andchemical constituents contained throughout the polyester substrate) andnon-barrier coatings materials that can be removed from polyesteraccording to the present invention can include, for example, saran,nylon, polyvinylidene chloride, acrylics, epoxy-based polymers,acetaldehyde scavengers, ethyl vinyl alcohol (e.g., EVOH films) and thelike.

The process of the present invention is also effective in removingentrained organic and/or inorganic compounds that may have been absorbedby polyester materials. Exemplary compounds can include, for instance,toluene, gasoline, used motor oil, paint, pesticide residues, and othervolatile compounds. Such compounds can often be absorbed by polyesterupon mere contact. For instance, polyester food and beverage containersare often misused by consumers after the food or beverage has beenconsumed. Specifically, the containers are sometimes used to holdvarious organic and/or inorganic compounds and solvents. When attemptingto recycle such polyesters, it is necessary to remove substantially allof the absorbed organic and inorganic compounds so that the polyestercan be once again reused as a beverage or food container.

Advantageously, regardless of the impurities present, the process of thepresent invention can include a first preparation stage includingremoving a portion of the contaminants via one or more physicalseparation processes followed by a reaction stage involving, in oneembodiment, contacting the mixture containing polyester with an alkalinecomposition, mixing the alkaline composition and the polyestercontaining mixture together such that the solids of the mixture aresubstantially and evenly coated by the composition and partialsaponification of the polyester occurs, heating the materials in a oneor multi-step process to a temperature sufficient to complete thesaponification reaction, if necessary, as well as to, among otherpossible benefits, preserve and/or enhance the physical properties ofthe polyester, and then purifying the polyester-containing mixturethrough various possible separation operations including, for example,washing the materials with a fluid, such as water.

A recovery process according to one embodiment of the invention will nowbe described in terms of one preferred example thereof which is setforth in FIG. 1. As illustrated in FIG. 1, the disclosed process can beconveniently referenced by delineation of the process into three stages,i.e., a preparation stage, a reaction stage, and a finishing stage. Itshould be understood, however, that this particular delineation is forconvenience in describing this embodiment, and is not to be considered arequirement of the disclosed process.

Preparation Stage

Prior to being separated from contaminants according to the presentinvention, the contaminated polyester materials can be, if desired,chopped or ground into flake form, for instance in a sizing operation.For purposes of this disclosure, the term polyester flake refers topolyester materials that have been chopped or ground into smallerpieces. Flaking of the materials can be done for the purpose offacilitating handling. It should be understood that all different sizesand shapes of material may be used in the process of the presentinvention and no one size or shape is required. For instance, in oneembodiment, the polyester can be in a discrete form, e.g., finelydivided or pelletized. Examples of post-sizing piece size can include,for example, pieces having a size of between about 1 and about 15 mm. Inone embodiment, the pieces can have a size of between about 0.125 andabout 0.75 in. The precise form of the pieces is not critical to thepresent invention.

In one particular embodiment, the polyester can be ground or choppedwhile the mixture containing the polyester is dry. While not wishing tobe bound by any particular theory, it is believed that chopping thematerials while in a dry state can improve the separation of certaincontaminants from the polyester substrates. For example, it is believedthat when multi-layered bottles are treated according to the disclosedprocess, dry grinding can facilitate the separation of the layers andthe removal of the coating material located between layers of polyesterin the multi-layered bottles.

Following any chopping or flaking of the polyester substrate, the drymixture containing polyester and contaminants can be subjected to one ormore operations for the removal of contaminants heavier than thepolyester. For example, according to one embodiment, the mixture can besubjected to an elutriation process specifically designed for theremoval of heavy contaminants, and in particular, metal contaminants.Elutriation is simply a process for separating heavier materials fromlighter materials by use of a directed stream of fluid flow (i.e., gasor liquid). Elutriation has been used in many processes includingrecycling processes in the past to remove lighter contaminants frompolyester. For example, elutriation operations are known throughoutrecycling processes for removing lighter label materials, such as paper,for example, from a mixture. In addition, elutriation operations can beused at various beneficial points throughout the process of the presentinvention for the removal of fines from the mixture.

According to one embodiment of the present invention, following anydesired chopping or grinding of the materials, an elutriation processcan be utilized to remove contaminants from the mixture that are heavierthan the polyester materials being recovered. More specifically, whereasin the past, it has been known to pull lighter contaminants off of thepolyester mixture via an elutriation process, according to thisparticular embodiment of the present invention, the mixture containingthe polyester can be the lighter stream separated during the elutriationoperation, and heavier contaminants, such as metal, rock, dirt, and thelike, can be removed from the mixture in the heavy stream pulled off ofthe elutriator. According to this particular separation operation, theelutriation fluid flow rate can be higher than that used in previouslyknown processes for separating lighter materials from apolyester-containing stream in order to separate heavier contaminantsthe from the polyester-containing mixture. For example, in oneembodiment, a fluid stream (e.g., air) flow rate between about 3600cubic feet/minute (cfm) and about 4600 cfm can be utilized in anelutriation process with an incoming solids flow of between about 2500pounds/hour (lb/hr) and about 3500 lb/hr in order to separate theheavier solids from the mixture containing polyester. In one embodiment,the incoming solids flow can be about 3000 lb/hr.

Referring again to FIG. 1, at some point during the preparation stage,for example following an elutriation process for removal of heavycontaminants, the mixture containing contaminants and polyester can becharged to a dry-cleaning vessel. In particular, the mixture ofmaterials charged to the cleaning vessel will contain at least somepost-consumer polyester and the mixture will be dry. That is, themixture will not be in a slurry form. The dry mixture of materials neednot be excessively dry, however. For example, the mixture need not bepre-treated to remove all moisture from the mixture, and the mixture canbe charged to the vessel at an atmospheric level of humidity.

The dry-cleaning vessel can include a cleaning chamber to which the drymixture is charged. In one preferred embodiment, this chamber can be atleast partially surrounded by a mesh with a predetermined mesh size. Itmay be preferred in some embodiments that the majority of the individualpolyester pieces charged to the dry-cleaning vessel be larger than theopenings of the mesh material in the cleaning vessel, to facilitatehandling of the mixture. Sizing of the materials prior to charging thematerials to the dry-cleaning vessel can also help to insure that atleast some contaminants are of a size to pass through the mesh, althoughmany contaminants can be degraded within the dry-cleaning vessel, asdescribed below.

In one embodiment, the chamber can include a series of blades spacedalong the axial length of the chamber. After being charged to thevessel, the materials can be induced to revolve or spin about thechamber axis, for instance due to the rotating action of the blades. Inparticular, the motion of the materials can be enough to fluidize thedry mixture. For example, the blades can rotate at a speed greater thanabout 20 m/sec, so as to fluidize the charged mixture. In oneembodiment, the blades can rotate at greater than about 2000 rpm. In oneembodiment, the tip speed of the blades can be between about 40 m/secand about 100 m/sec, for instance, about 50 m/sec. In anotherembodiment, the tip speed of the blades can be between about 60 m/secand about 80 m/sec.

In addition to fluidizing the mixture, the rotation of the mixturecaused by the rotating blades can also encourage dynamic collisionsbetween the materials in the mixture and the chamber wall. Collision ofmaterials contained in the mixture with the wall can lead to thedegradation of contaminants in the mixture, and in particular,degradation of the contaminants to the point that the individual piecescan be smaller than the mesh size of the surrounding wall. In addition,these dynamic collisions can facilitate physical detachment of embeddedor otherwise attached contaminants from the polyester. Upon collisionbetween suitably small contaminants (smaller than the mesh size of thewall) with the mesh, the contaminants can pass through the surroundingmesh, and the polyester can remain in the chamber. The rotation of theblades can also facilitate airflow through the chamber and the movementof the materials from one end of the chamber to the other.

Surprisingly, the dry-cleaning operation can physically separatepolyester from attached contaminants, including embedded contaminants,as well as degrade many brittle contaminants, without substantialdegradation of the polyester. For example, while coating materials, suchas paper label materials or vapor barrier coatings, and embeddedmaterials, such as embedded glass and dirt, can become detached from thepolyester substrate during the dry-cleaning operation, the polyesterflakes themselves can remain essentially the same size and shape asoriginally charged to the vessel. In addition, while contaminants can beseparated from the polyester and pass through the surrounding mesh, thepolyester can remain within the cleaning chamber. Even in thoseembodiments in which the polyester includes polyester flakes of a sizesmaller than the mesh openings, the bulk of the small polyester finescan remain suspending in the cleaning chamber and not be lost with thecontaminants during the separation process.

While not wishing to be bound by any particular theory, it is believedthat due to the centrifugal forces acting on the suspension, thematerials within the mixture can separate, with the denser materials,and in particular, contaminants such as glass, metal, paper, and thelike, moving to the outside of the mass, while the lighter materials,and particularly the small polyester fines, can remain suspended closerto the center of the chamber. Accordingly, glass-like materials andfibrous materials can degrade and pass through the screen at the outeredge of the mass, while elastomeric materials, such as PET can remainbehind. As such, even PET particles smaller than the screen orifice canremain with the main rotating body, and very few polyester fines willpass through the screen, and high yield of polyester can exit thedry-cleaning operation.

The dry-cleaning operation can be particularly effective at removingglass from a mixture including both glass and polyester. Glass has oftenbeen considered to be one of the most difficult materials to separatefrom post-consumer polyester during a polyester recycling process andcan be detrimental to the process if not completely removed. Glass thatis not removed during the recycling process can not only cause seriousdamage to processing equipment during the recycling process, but it canalso destroy the materials to be formed from the recycled polyester. Forexample, glass that is not removed during the recycling process canbecome incorporated with the polyester during a subsequent materialformation process (e.g., a beverage container formation process) and candestroy the materials to be formed from the polyester through, forinstance, the formation of holes in the polyester products.

According to one embodiment of the present process, more than about 97%of the glass in a mixture containing both glass and polyester can beremoved from the mixture during the disclosed dry-cleaning operation. Inone embodiment, more than about 98% of the glass in a mixture can beremoved. In another embodiment, more than about 99% of the glass can beremoved during the dry-cleaning operation.

During the preparation stage, for example either prior to or followingthe dry-cleaning operation, the mixture can be further processedaccording to one or more additional dry separation operations. Forexample, in one embodiment, the mixture can be subjected to anelutriation operation for removing light contaminants from the mixture.For instance, the airflow through the elutriator can be between about1500 cfm and about 3000 cfm for a solids flow of about 3000 lb/hr and atleast a portion of the lighter contaminants can be removed from themixture. Other dry separation operations that can optionally be includedat one or more locations in the preparation stage include any separationoperations generally known in the art such as, for instance, screeningoperations utilizing vibratory screens for separation of contaminantslarger or smaller than the polyester, depending upon the mesh size ofthe screen and the size of the polyester flakes.

During the preparation stage, the mixture can also be subjected to oneor more aqueous separation operations. For example, in the embodimentillustrated in FIG. 1, an intensive washing operation can follow thedry-cleaning operation and the elutriation operation. Beneficially, dueto the prior separation operation(s), the aqueous separation operations,e.g., the intensive wash operation, that can follow can describe lowercontamination levels in the wash water, and hence less wastewatertreatment processing can be required by the process. In particular, asmany contaminant materials and impurities can be removed by the abovedescribed dry separation operations, problems encountered in the pastwith aqueous separation techniques, such as congealing of separatedcoating materials, or expensive water treatment requirements, forexample, can be less of a problem in the polyester recovery process ofthe present invention.

For example, following the dry-cleaning operation, with or without anyadditional separation operations, such as elutriation, for example, thewash water can show a decrease in chemical oxygen demand of at leastabout 15%, as compared to wash water used directly on the contaminatedpolyester materials. Similarly, through use of at least the dry-cleaningoperation prior to the aqueous wash, the total dissolved solids level ofthe wash water can decrease by about 30%, total suspended solids candecrease by at least about 50%, and oil and grease can decrease by about15%.

An intensive washing step can include adding water to the mixture andsubjecting the materials contained in the aqueous mixture to high shearso as to facilitate the removal of certain contaminants, such asoligomers, and other organic and inorganic compositions from the surfaceof the polyester. In general, a high shear wash can include those inwhich the turbulence of the wash water during the operation is greaterthan a standard wash, but low enough to prevent excessive flake damageand/or fines formation. For example, a high shear wash according to thepresent invention can include those in which the wash rotors rotate witha tip speed of between about 500 and about 1000 feet per second (fps).Such high shear washers are commercially available in the art frommanufacturers such as Reg-Mac, Sorema, or B&B.

According to another aqueous separation operation suitable for use inthe disclosed process, the materials containing the polyester can beimmersed in water such that the less dense or lighter materials can beseparated from the heavier materials, and specifically from thepolyester. More particularly, it is known that polyester sinks in waterwhile other polymers, such as polyolefins, and paper products are waterbuoyant. Thus, the lighter materials can be easily separated from theheavier materials when contacted with a suitable amount of water.Subjecting the materials to a sink/float separation step and removalfrom the mixture of some of the contaminants not only can reduce thequantity of materials in the mixture being processed but can also helpto clean the materials prior to further processing.

When delivering the mixture containing contaminants and polyester to asink/float tank, it may be beneficial in certain embodiments to deliverthe mixture below the liquid surface. This can eliminate the effect ofsurface tension of the water in the tank on the materials contained inthe mixture, and facilitate the sinking of the denser materials in thetank.

In order to further improve the disclosed process, and in particular, inorder to decrease the amount of water used in the process, thepreparation stage of the process can also include a recirculation tankfor recirculating the water used in, for example, the intensive washerand/or the sink/float tank. Accordingly, any water used in the aqueousoperations of the preparation stage, as well as any water removed fromthe materials during any drying operations at any stage of the process,can be recirculated through the recirculation tank. In addition, therecirculation tank can include an agitator, if desired, so as tomaintain in suspension any polyester fines carried over into therecirculation tank, and thus facilitate the reintroduction of thesepolyester fines back into the main stream of the decontaminationprocess.

Other aqueous separation operations that can optionally be utilized inthe preparation stage of the process can include, for example,utilization of one or more hydrocyclone separators as are generallyknown in the art. For example, a single hydrocyclone, doublehydrocyclones, or multiple hydrocyclones can be utilized in series forseparating contaminants from the mixture containing polyester.

Following the aqueous preparation operations, e.g., the intensive washand the sink/float separation step, the mixture containing polyester andremaining contaminants can be dried and optionally subjected toadditional dry separation operations prior to being combined with analkaline material during the reaction stage of the process. This dryingoperation can, for example, occur at temperatures not greater than about160° C. For instance, in one embodiment, drying can occur at betweenabout 130° C. and about 160° C., and can generally be carried outaccording to any method as is generally known in the art.

For instance, according to the embodiment illustrated in FIG. 1, priorto the reaction stage, the mixture can be dried and then subjected to acolor sorting operation. Utilization of a color sorting operation priorto the reaction stage of the process has been found beneficial incertain embodiments of the present invention as the operation canessentially function as another cleaning step in the process, removingvarious contaminants from the mixture and thus ‘cleaning’ the mixtureprior to the reaction stage. Contaminants that can be removed from themixture prior to the reaction stage via a color sorting operation caninclude, for example, metals and colored polymeric components such aspolyester materials colored with titanium dioxide.

In general, colored polyester materials, and in particular, whitepolyester materials colored with titanium dioxide cannot be efficientlyrecycled, as they are considered contaminants of the desired clearproduct stream. As such, it is beneficial to remove such materials fromthe recycle stream. In the past this has proven difficult, however, asduring the recycle process itself, the clear polyester feed materialscan be crystallized and appear white, and therefore difficult toseparate from white contaminants such as the polyester/TiO₂ materials.According to the presently disclosed process, such materials can beseparated from the stream prior to the reaction stage, and thus, priorto the possible crystallization of the recyclable polyesters.

In general, any color sorting technique as is generally known in the artcan be utilized in the disclosed invention. For example, visualinspection or automated optical sorting and separation techniques can beused. Examples of commercially available optical color sorting equipmentcan include those produced by manufacturers such as SRC, Satake, andMSS.

Other separation operations that can be utilized in the presentinvention, for instance during the preparation stage of the process toremove as many contaminants as possible prior to the reaction stage, caninclude, for example, aqueous separation processes such as additionalelutriation processes, additional washing operations, additionalscreening processes, and/or the utilization of operations specificallydesigned for the removal of metals from the stream.

Metal removal processes suitable for use in the present invention caninclude the use of magnetic separators, such as drum magnets, waterfallstyle magnets, eddy-current machines, or any other suitable magneticmetal detectors and separators such as those available from BuntingMagnetics, Co. of Newton, Kans. or S&S Recycling GmbH of Germany. Suchdevices can utilize any type of magnet (e.g., permanent ferrous magnets,rare earth magnets, electromagnets) in any suitable design so as toremove at least a portion of metallic contaminants contained in themixture.

Reaction Stage

During the reaction stage of the disclosed process, a portion of thepolyester in the mixture can be saponified through reaction of thepolyester with an alkaline compound. More particularly, the reactionstage of the process can include one or more mixers, at least one ofwhich can be a high-energy mixer. In addition, the reaction stage canoptionally include additional reaction operations, such as a hightemperature heat setting operation.

For instance, and according to the embodiment illustrated in FIG. 1, thereaction stage of the process can include a first low-energy mixingoperation, in which the mixture containing polyester and contaminantscan be combined with an alkaline composition prior to being fed to ahigh-energy mixing operation, in which a portion of the polyester can besaponified. Following the high energy mixing operation, the mixture canbe dried and fed to a heat setting operation, for example utilizing akiln, in which, among other benefits, the saponification reaction can becompleted, if necessary. In addition, during the heat setting operation,secondary materials can be further reacted with the alkaline compositionand the physical properties of the polyester can be preserved and/orenhanced.

The reaction stage of the process can optionally include one or moreprocesses for the recovery of reaction byproducts. For example, uponsaponification of PET, the reacted polyester material can be convertedinto a metal terephthalate and ethylene glycol. If desired, the metalterephthalate that is thus produced can be dissolved in water and thewater can be acidified, causing terephthalic acid to precipitate. Theterephthalic acid can be filtered and recovered as a byproduct of thedisclosed process, if desired. Similarly, the polyol that is formedduring the reaction process can either remain as a liquid within themixture for later removal, or can be directly evaporated if the reactionoccurs at conditions that facilitate the evaporation of the polyol. Thepolyol can then be recovered, if desired, for instance by use of acondenser.

The alkaline compound selected for mixing with the materials can be, inone preferred embodiment, sodium hydroxide, known commonly as causticsoda. Other metal hydroxides and alkalines can optionally be used inaddition to or instead of sodium hydroxide, however. For example,suitable compounds can include calcium hydroxide, magnesium hydroxide,potassium hydroxide, lithium hydroxide or mixtures thereof. When used insolution, the metal hydroxide can be combined with water prior to mixingwith the materials containing the polyester. For instance, in oneembodiment, the metal hydroxide can be mixed with water in about a 1 to1 ratio.

In general, the reaction stage of the present invention includes ahigh-energy mixing step during which the mixture containing contaminantsand polyester can be combined with a selected amount of an alkalinesolution to form a slurry. The amount of the alkaline composition addedto the materials containing the polyester will generally depend upon thetype and amount of impurities and contaminants present within thematerials. Generally, the alkaline composition should be added only inan amount sufficient to separate the impurities from the polyester, soas to minimize the saponification of the polyester. In mostapplications, the alkaline composition can be added to the materials ina stoichiometric amount sufficient to react with up to about 50% of thepolyester. Preferably, the alkaline composition is added in an amountsufficient to react with less than 10% of the polyester and mostpreferably around 3% of the polyester.

In the embodiment illustrated in FIG. 1, the slurry can be formed in afirst low-energy mixer, but this is not a requirement of the invention.In other embodiments, the slurry can be formed directly in thehigh-energy mixer, and the low-energy mixer may not be included.Optionally, a surfactant or wetting agent may be added to the mixtureand the alkaline composition when forming the slurry. Addition of asurfactant can facilitate the mixing of the alkaline composition withthe materials, reducing the amount of the alkaline composition thatneeds to be added. The surfactant should be alkaline stable and can benonionic or anionic in character. An example of a suitable surfactant isETHAL TDA-3, a nonionic surfactant marketed by Ethox, Inc. ofGreenville, S.C.

In those embodiments wherein one or more low-energy mixers are utilizedfor formation of the slurry, certain low-energy reactions can also takeplace in the mixer. For example, when utilizing a low-energy mixingoperation, the mixer can optionally be utilized at operation parameters(for example, with the addition of a small amount of thermal energy, viaheating of the mixer) so as to encourage reaction of the alkalinecomposition with certain contaminants found in the mixture, and in oneparticular embodiment, with aluminum. However, in those embodimentswherein additional energy is added to the mixture in the low-energymixer so as to promote reaction between contaminants and the alkalinecomposition, the total amount of energy added to the mixture at thispoint in the process should not be great enough to promote anysaponification reaction between the polyester and the alkalinecomposition. For example, in one embodiment, the low-energy mixer can beoperated at an internal temperature of between about 90° C. and about110° C. so as to encourage reaction between any aluminum contained inthe mixture and the alkaline composition without promoting asaponification reaction between the polyester contained in the mixtureand the alkaline composition.

It has been found that at low-energy conditions, such as those that canbe encouraged in a low-energy mixer, the alkaline composition can reactwith aluminum in the mixture to form, for example, an alkali aluminumsalt that can be dissolved in the water of the slurry. Thus, in certainembodiments of the present invention, a low-energy mixer can be utilizedprior to any saponification of the polyester contained in the mixture toform a slurry and efficiently coat the solids of the mixture with thealkaline composition as well as to promote reaction of the alkalinecomposition with various contaminants contained in the mixture.

Optionally, a rinsing or washing operation can be included in theprocess following the low-energy mixer, for instance to remove anyreaction products formed in the low-energy mixer. For example, in thoseembodiments wherein aluminum is reacted with the alkaline composition inthe low-energy mixer to form an alkali aluminum salt, the mixture can berinsed to remove at least a portion of the salt prior to additionaloperations in the reaction stage of the process.

Following any optional low-energy mixing operation, the materials can befed to one or more high-energy mixers. As previously mentioned, in thoseembodiments not utilizing a low-energy mixer for formation of theslurry, the slurry can be formed in the high-energy mixer itself.Moreover, alkaline composition can be added to the mixture in the highenergy mixer, not only in those embodiments when the slurry is formed inthe high energy mixer, but also when the alkaline-containing slurry hasbeen rinsed to remove contaminants prior to flow into the high energymixer or to replace alkaline composition that has reacted withcontaminants in the low-energy mixer, whether rinsing has occurred ornot.

The high energy mixer utilized is one that can not only providesubstantially complete and even coating of the polyester materials bythe alkaline composition, when desired, but also can impart sufficientenergy to cause a portion of the polyester to saponify, or, in otherwords, to hydrolyze, without the necessity of the addition of largeamounts (or in certain embodiments, any) heat to the mixer. For example,mixers such as those described in U.S. Pat. No. 4,320,979 to Lucke andU.S. Pat. No. 4,189,242 to Luke, which are herein incorporated in theirentirety by reference thereto, may be employed in the high-energy mixingoperation to promote saponification of at least a portion of thepolyester with the alkaline solution.

In one embodiment of the present invention, a high-energy mixer can beoperated at a Froude number greater than about 4.2, particularly greaterthan 6.6, and more particularly greater that about 9.5. Specifically, atthe above rates, the mixer of the present invention not only mixes theslurry but also imparts sufficient energy to the slurry to cause thealkaline composition to react with the polyester. In one embodiment,high energy mixing can be continued until substantially all of thealkaline composition has been exhausted. For example, the high-energymixer can be operated such that residual (unreacted) metal hydroxideexiting the mixer can be less than about 1% by weight of the slurry.Specifically, residual metal hydroxide exiting the mixer can be lessthan about 0.5% by weight. More specifically, residual metal hydroxidecan be less than about 0.1% by weight of the slurry, for instance lessthan about 0.05% by weight.

During saponification, various coatings that may be adhered to thepolyester and/or other contaminants which may be entrained within thesurface of the polyester can be released from the polyester. The energyprovided from the action of the mixer can also promote reaction betweenthe alkaline solution and other contaminants that can be found in theslurry, such as polyvinyl chloride or aluminum, for example. Uponreaction of these types of materials with the alkaline composition, theimpurities can be converted to another form, one which is more easilyseparable from the polyester substrate.

In addition, it is also believed that due to the completeness of mixingas well as the substantially even coating of alkaline supplied to thepolyester materials in the high energy mixer, the salt reaction productcan form a coating on the polyester materials which exit the mixer. Forexample, if the outer surface of a PET flake is saponified in thehigh-energy mixer with a sodium hydroxide composition, it is believedthat the disodium terephthalate reaction product can coat the remainingPET. Moreover, it is believed that this coating formed around apolyester piece can serve to protect the polyester during laterprocessing operations. For example, the salt coating can protect thepolyester from oxidation due to high temperature conditions encounteredlater in the heat setting operation. Among other benefits, this canprovide a polyester product with less discoloration than that obtainedin the past.

In certain embodiments, following reaction in one or more high-energymixers the mixture can be dried and proceed to the finishing stage oroptionally proceed directly from a high-energy mixer to the finishingstage. In particular, in those embodiments wherein the recycledpolyester product obtained from the process is not intended asfood-grade product, additional reaction operations, and in particular,the heat setting operation discussed below, may not be necessary. Inthose embodiments wherein food-grade product is desired, however, theprocess can include at least one heat setting operation.

Following the reaction within the high-energy mixer, the slurry can thenbe dried and, in certain embodiments, fed to a heat setting operation.For example, the mixture can first be dried by heating the mixture to atemperature of between about 150° C. and about 160° C., followed byadditional heating, after drying, to a heat setting temperature that canencourage additional reaction of the materials. The actual temperatureto which the mixture is heated during the heat setting operation candepend upon a number of factors. In general, the mixture should beheated to as high a temperature as possible without melting thepolyester. For instance, PET has a melting point typically between 250°C. to about 270° C. Consequently, when substantial amounts of PET arecontained within the materials, the mixture should be heated to atemperature below about 270° C. during the heat setting operation. Inmost applications, the temperature can be within a range of from about100° C. to about 270° C.

In general, the heat setting operation can be carried out in anenvironment that is at least substantially free of water, for example,in a dry air environment. However, though a dry air environment can bepreferred in some embodiments, due to, for example, cost considerations,an inert atmosphere such as nitrogen, argon, carbon dioxide, or the likecan also be effectively employed, such as in the form of a nitrogenblanket. If desired, the mixture can also be heated at reducedpressures, which correspond to lower oxygen levels. By the term “atleast substantially free” it is meant that the amount of water presentin the environment is less than that which results in degradation of thepolyester during heating. This amount is typically not more than 80 ppm(−40° F. Dew Pt.), preferably not more than about 10 ppm, still morepreferably not more than about 5 ppm (−80° F. Dew Pt.). There is notheoretical minimum as the amount of water can be as low as 1 ppm of theenvironment or even less.

Also, in one embodiment, the mixture can preferably be heated in anoxygen-starved environment. As used herein, oxygen-starved refers to anenvironment in which oxygen is present below about 19% by volume. Incombination with the dry atmosphere, maintaining lower oxygen levelsduring the heat setting phase can further prevent the polyester frombeing substantially degraded or discolored and also can further preventagainst uncontrolled combustion. If desired, the mixture can also beheated at reduced pressures, which correspond to lower oxygen levels. Inaddition, during heating, the slurry can generally be heated indirectlysuch that it does not contact an open flame.

An oxygen-starved environment is not a requirement of the invention,however, and in other embodiments, it may be preferable to heat themixture in an oxygen-rich environment, i.e., an environment includingoxygen at greater than about 19% by volume.

The equipment and apparatus used during the heat setting operation ofthe present invention can vary. For example, in one embodiment the heatsetting operation can be carried out in a rotary kiln. The rotary kilncan be heated by an electrical element, by heated oil or by fossil fuelburners. One example of a suitable indirectly heated kiln for use in theprocess of the present invention is the Rotary Calciner marketed by theRenneburg Division of Heyl & Patterson, Inc. In other embodiments,however, a multi-disc thermal processor or an oven can optionally beemployed. Of course, many other similar devices, for example, infraredheat processors, microwave heaters, and the like are available that mayoptionally be utilized in the processes of the present invention.

In one embodiment, the kiln can first be heated to a lower temperaturefor a desired period of time to dry the materials from the high-energymixer and then the temperature can be increased to the higher level.Alternatively, the slurry exiting the high-energy mixer can first beheated in a dryer, such as, for example, a ConAir dryer, before beingtransferred to a kiln for the higher temperature heat setting step. Inyet another embodiment, a kiln can be utilized for relatively rapidtemperature increase of the mixture to the desired level, and the hotmaterials can then be transferred to a larger column dryer or any othersuitable solid stating system, where they can be maintained at thedesired temperature for the desired period of time.

The heat setting operation of the disclosed process can provide manybeneficial functions. For example, during the heat setting operation,by-products such as ethylene glycol formed during the saponificationreaction in high energy mixing either the high-energy mixer or in theheat setting operation can be evaporated off of the stream. Theevaporated materials can then be collected, for instance in a condenser,and sent to a suitable treatment operation, for instance a watertreatment operation for recovery, if desired. In addition, during theheat setting operation any remaining unreacted alkaline that has beencarried over from the high energy mixing operation can be reacted witheither polyester or other reactive contaminants found in the mixture.

Remaining entrained organic and/or inorganic compounds that may beabsorbed into polyester can be removed from the product polymer duringthe heat setting process. Specifically, any remaining volatile organicand inorganic compounds can be substantially removed during the heatsetting step not only from the polyester, but also, and depending uponthe nature of the compound, from the stream altogether via theoff-gases. By ensuring removal of substantially all of any entrainedorganic and inorganic compounds, “food grade” polyester can be recoveredwhich can be used in an unrestricted manner. In addition, heating themixture can cause loose, dried impurities to be degraded into a moreeasily separable form in order to facilitate final separation of theimpurities from the polyester product.

The heat setting operation can also improve the physical characteristicsof the polyester in the mixture. In particular, the heat settingoperation is believed to increase the clarity and the intrinsicviscosity of the product polyester materials. To this end, the heatingstep in the presence of a dry atmosphere can be performed for a periodof time sufficient to enhance the intrinsic viscosity of the polyester.For example, according to one embodiment of the presently disclosedprocess, the intrinsic viscosity of a polyester in the feed can increasefrom about 0.76 dL/g to about 0.82 dL/g. For instance, the intrinsicviscosity of the feed materials can be increased by between about 5% andabout 10% according to one embodiment of the presently disclosedinvention. A minimum time is dependent on, e.g., the water content ofthe environment and can be as low as 5-10 minutes.

Once physically separated from the polyester, contaminants such as thenow detached coatings materials and/or entrained materials can befurther degraded while the materials are processed in subsequentoperations. For instance, solvents and liquids contained within thecoatings or removed from the polyester during the heat setting operationcan be volatilized and optionally removed from the kiln and recapturedin a condenser similar to the method for recapturing the ethylene glycolproduct from the saponification reaction described above. Left behind inthe mixture can be some relatively smaller sized impurities. When themixture is later subjected to additional separation operations, forinstance in the finishing stage of the process, remaining insolubleimpurities can be separated from the larger polyester chips, forinstance using an appropriately sized screen that allows passage of theimpurities while preventing passage of the polyester.

During the reaction stage of the process, in addition to saponifying aportion of the polyester, certain hard-to-separate contaminants commonlyfound with post-consumer polyester can be converted into a form that canbe more easily separated from the mixture. In particular, during thereaction stage of the process contaminants such as polyvinyl chloride,polylactic acid (PLA), and aluminum can be converted into forms that canbe more easily separated from polyester.

When polyvinyl chloride and/or polylactic acid are present within thematerials, the materials can be converted into a form that is moreeasily separable from the mixture. For example, according to oneembodiment, at least a portion of the PVC can be converted to a formthat is darker and thus separable from the mixture via color sortingtechniques. In some embodiments, the PVC contaminants can be convertedto a form that floats in water. In other embodiments, the PVC can bereacted to a form that exhibits increased heat resistance. Moreover,combinations of these characteristics can be exhibited by the reactedPVC. In general, the specific reactions of the PVC with the alkalinecomposition can depend upon the particular characteristics of the PVCcontaminants contained in the mixture. However, no matter what theparticular starting characteristics of the contaminant PVC, it isbelieved that upon combination of the mixture with the alkalinecomposition and addition of suitable energy, the PVC can react to formmore easily separable from the polyester contained in the mixture.Consequently, when polyvinyl chloride is present in the materials, itmay be preferable to add enough alkaline composition to the slurrysufficient to react with the polyvinyl chloride or, in other words, toconvert the polyvinyl chloride into a form separable from the polyester.

However, if not reacted with the alkaline composition in the high energymixer and/or during heat setting, the PVC can optionally be removed fromthe mixture by heating the mixture to a temperature that is greater thanthe melting temperature of PVC but less than the melting temperature ofthe polyester contained in the mixture, upon which the PVC can melt andthen be removed from the mixture, for instance by use of a sieve orother suitable separation technique during either the reaction stage oroptionally during the finishing stage of the process.

PLA can be removed from the mixture according to similar processes asthat described above for PVC. In particular, any variations in theprocess, for example, variations in amount of alkaline composition,variation in processing conditions (e.g., temperatures, etc.) that maybe different from those described above for PVC are well within thegeneral knowledge of one of ordinary skill in the art, and thus will notbe described in detail herein.

Besides polyvinyl chloride, polyester collected from the solid wastestream can also typically be mixed with pieces of aluminum, as mentionedabove. The aluminum can originate, for instance, from bottle capsutilized with polyester beverage containers or from the imperfectseparation of plastic and aluminum cans found in post-consumer waste.Aluminum, similar to polyvinyl chloride, cannot easily be separated frompolyester using standard separation processes such as a sink/floatseparation operation.

When contacted with an alkaline composition and provided with suitableenergy within any or all of the low-energy mixer, the high-energy mixerand/or the heat setting operation, aluminum can be converted to analkali aluminum salt, which is typically water soluble. Thus, in oneembodiment, an amount of alkaline composition can be added to thematerials containing polyester and aluminum sufficient to completelyconvert the aluminum to an aluminum salt. Following the reaction, afluid, such as water, can then be added to the mixture to dissolve thealuminum salt and separate it from the polyester.

According to one embodiment of the present invention, not all of thealuminum contained in the stream entering the reaction stage need beconverted into an aluminum salt. Instead, only a portion of the aluminumcan be converted to the aluminum salt with the alkaline composition. Inparticular, it has been discovered that following the reaction of aportion of the aluminum with the alkaline composition, the remainingaluminum pieces can become brittle. According to this embodiment, thematerials containing the polyester mixed with the remaining aluminum canthen be agitated under shear conditions and the remaining brittlealuminum can be broken into small pieces. The small pieces can then beseparated from the polyester for instance with a suitable separationoperation, for instance, a simple screening process utilizing a screenhaving a size sufficient to capture the larger polyester chips whileallowing the smaller broken aluminum pieces to pass.

Accordingly, when aluminum is present within the materials containingthe polyester, the alkaline composition can be added to the materials inan amount sufficient to react with at least a portion of the aluminum,sufficient that the remaining aluminum will be brittle. Of course, theactual amount of alkaline composition added can depend not only upon thequantity of aluminum present in the materials, but also upon the size(e.g., thickness) of the aluminum pieces.

Additional operations that can be included in the reaction stage caninclude, for example, additional heating operations, for instanceholding the mixture at a suitable temperature for a period of time tofurther increase the intrinsic viscosity of the product polyester. Forexample, following a heat setting operation at high temperature, forinstance in a kiln, the mixture can be held in one or more ovens for aperiod of time at a desired temperature to ensure the production offood-grade polyester, to further improve the physical characteristics ofthe product, to remove additional volatile contaminants, and/or toremove additional non-volatile contaminants, such as paper fibers, forexample, via heat convection and/or radiant heat in the oven. Anysuitable oven can be used in such an embodiment, including infrared typeovens.

Finishing Stage

Particular operations included in the finishing stage of the disclosedprocess can generally vary depending on the particular contaminantsand/or impurities in the starting compositions. In addition, anddepending upon the particular impurities found in the starting material,the invention can not only effectively recover polyester from a varietyof contaminants and/or impurities, but can also recover particularcontaminants found in the waste stream as by-products of the process.For example, polyolefins removed from the stream at a sink/floatoperation can be dried and recovered.

In one embodiment, the finishing stage of the process can at the veryleast include at least one washing or rinsing operation, one colorsorting operation, for removal of discolored contaminants from themixture, and at least one elutriation operation, for the removal offines and any remaining light contaminants from the product.

Optionally, rather than or in addition to simply washing the materialswith water, the materials can be washed with a cleaning solution. Forinstance, the mixture containing the polyester and any remainingcontaminants can be mixed with a hot aqueous solution containing asurfactant or with a hot aqueous solution containing an alkalinematerial and washed. If desired, the mixture can be heated underagitation or in a high intensity wash, such as that described aboveduring the preparation stage. Washing the materials can clean thepolyester by straight separation of the polyester from the contaminantsand can also dissolve and/or break apart some of the contaminants.

During the finishing stage, the acid salt or metal salt formed duringthe saponification reaction can dissolve in the wash water. If desired,the metal salt can be later recovered from the wash water for disposalor as a by-product of the process. For instance, if the acid salt is aterephthalate, the wash water can first be filtered in order to removeany undissolved impurities and contaminants. Next, the wash water can beacidified causing terephthalic acid to precipitate. In order to acidifythe solution, a mineral acid such as hydrochloric acid, phosphoric acidor sulfuric acid or an organic acid such as acetic acid or carbonic acidcan be added to the solution. Once the terephthalic acid precipitates,the terephthalic acid can be filtered, washed and dried, leaving arelatively pure product.

In order to separate certain contaminants, such as certain polyvinylchloride reaction products, from the polyester, the mixture can becombined with a fluid such as water during the finishing stage. Whenplaced in water, the polyester will sink while the dechlorinatedpolyvinyl chloride can float. In addition, it has been found thattreating polyvinyl chloride with an alkaline composition in theabove-described manner can promote the adhesion of entrained air andother gas bubbles to the surface of the polyvinyl chloride reactionproduct, making the polyvinyl chloride reaction product even morebuoyant. Consequently, when the mixture is in liquid (e.g., water) gasbubbles, such as air bubbles, may be forced through the liquid toincrease separation efficiency. Of course, other separation techniquesbased on the differences in density between the polyester and thedechlorinated polyvinyl chloride may optionally be incorporated into theprocess.

As described above, the reaction of PVC with the alkaline compositioncan also darken the color of the polyvinyl chloride and increase itsmelting point. Consequently, in another embodiment, the polyvinylchloride reaction product can be separated from the polyester during thefinishing stage via a color sorting operation, such as that describedabove in the preparation stage. Other contaminants can be separated fromthe mixture via a color sorting operation during the finishing stage aswell. For example, in certain embodiments, the polyester feed productcan include certain barrier materials, such as acetaldehyde scavengerbarrier materials in either the reacted or unreacted form. According tothe present invention, such contaminants can become discolored duringthe presently disclosed process, for instance during the heat settingoperations of the present invention. Upon a color sorting operationduring the finishing stage, such contaminants, and in particular, thosethat can alter in color during the reaction stage of the process, can beremoved from the mixture.

In one embodiment, the finishing stage can include neutralization of anyremaining alkaline material through the addition of a suitable acid tothe mixture such as an inorganic acid including, for example,hydrochloric acid, phosphoric acid and/or sulfuric acid or an organicacid such as acetic acid and/or carbonic acid. Following neutralizationof any remaining base through addition of an acid solution, the mixturecan be dried prior to any dry separation operations.

During the finishing stage, remaining metal contaminants can be removedfrom the mixture in a metal removal operation. One embodiment of a highquality metal removal operation suitable for use in the presentinvention is illustrated in FIG. 2. As can be seen with reference toFIG. 2, according to this particular embodiment, a metal removaloperation can include multiple metal detectors in series and parallelcombination to form a bank of individual metal removal devices so as toprovide more complete removal of metal contaminants than obtained inmetal separating operations known in the past.

It should be understood that though this particular metal separationoperation is presented herein as an operation taking place during thefinishing stage of the disclosed process, an equivalent operation couldoptionally be included elsewhere in the process, for instance during thepreparation stage. In addition, multiple high quality metal removaloperations as herein described can be included in a polyester recoveryprocess at various suitable locations throughout the process.

In one embodiment, the process can include multiple banks of two or moremetal removal devices in a single operation step. According to thisembodiment, the total mixture stream can be split among two or morebanks of metal removal devices, so as to create multiple smaller inputstreams to each bank of devices. For example, a single operative step ina polyester recovery process can include one, two, or even more banks ofdevices. For instance, the high quality metal removal operation caninclude anywhere from 1 to 10, 20, 30, or even more banks eachcontaining two or more individual metal detection and removal devices.

Referring to FIG. 2, a single bank of devices according to oneembodiment of the invention is illustrated. As can be seen, according tothis particular embodiment, the bank includes five individual metaldetection and removal devices, but it should be understood that thisparticular number is not a requirement of the invention. In otherembodiments, the bank of devices can include additional or optionallyfewer individual devices. For instance, the bank of devices can includeas few as two devices and no limit to the upper number of individualdevices included in the bank. Though practically speaking, economicconsiderations can generally be involved in determining the preferrednumber of individual devices included in a bank as well as the totalnumber of banks included in an operative step of the process.

The entire input stream fed to the bank is treated in a first metaldetection unit 1. Upon detection of metal in the input stream, a portionof the stream including the detected metal is separated and removed fromthe stream, as rejected stream 10. The ‘clean’ or accepted stream 7 andthe rejected stream 10 taken off of metal detection unit 1 then proceedto additional metal detection units 2, 5, respectively. At metaldetection unit 2, the detection and separation process is repeated, withthe rejected stream 11 (which includes detected metal) being fed tometal detection unit 5, and the accepted stream 8 being fed to yetanother detector and separation unit 3, and then on to final metaldetection unit 4. The rejected streams 12, 13 from metal detection units3 and 4 are each fed to the recycle stream 6, and the final acceptedstream 18 continues on in the overall process. At metal detection andremoval unit 5, the accepted stream 20 is fed back to recycle stream 6,and the rejected stream 14 is removed from the process as waste materialcontaining metal.

In addition to recycling the rejected streams 10, 11, 12, 13, andaccepted stream 20 back through the process via recycle stream 6, theindividual metal detectors contained in the bank can be set atincreasing sensitivity as the stream proceeds through the process, asshown by the side arrow. For example, metal detection units 2, 3 and 4can have increasing sensitivity as compared to each other as well ascompared to metal detection unit 1. Moreover, the sensitivity of metaldetection unit 5 can be greater than that of metal detection unit 1.

Through the process of the present invention including the high qualitymetal removal operation, essentially all metal contained in the inputstream of the process can be removed from the polyester product stream.

In general, the finishing stage of the operation can also include one ormore elutriation operations for the removal of any remaining lightcontaminants such as any remaining paper or paper fibers or any polymerfines.

Other separation operations that can be utilized in the finishing stageas well as between operations in the preparation and/or reaction stagecan include physical separation operations such as those described abovein regard to the preparation stage as well as any other suitableseparation operations as are generally known in the art such as, forinstance, the use of one or more destoning operations for the removal ofglass, and/or the use of hydrocyclones. For example, in one embodiment,a double hydrocyclone embodiment can be utilized in which the materialscan be pumped to a first hydrocyclone to remove high-densitycontaminants, such as glass and/or metal, and then sent to a second tankand pumped to a second hydrocyclone to remove lower-densitycontaminants, such as paper and/or polyolefins, for example.

One or more vibratory screening methods can also be utilized at variouslocations throughout the disclosed process to, for example, separatecontaminant materials taken off of the top of the sink/float tank fromthe processing water, for removal of contaminants in powdered formfollowing the heat setting operation, following a high shear washingoperation in the preparation and/or finishing stage or following a finalwashing and drying operation in the finishing stage.

In one embodiment, heavy contaminants can be removed from the mixture atany suitable point in the process by use of a sluice operation. Forexample, immediately before or after any aqueous separation operationsin the preparation stage or immediately before or after any aqueousseparation operations in the finishing stage, it may be beneficial incertain embodiments of the process to include a sluice operation for theremoval of certain heavy contaminants from the mixture.

The treatment method of the disclosed invention is capable of providinga number of significant advantages. For example, it is capable ofcleaning and/or decontaminating polyester. In fact, the polyester can becleaned and/or decontaminated to a level which is sufficient to meetvarious regulatory guidelines, and in particular, can produce food-gradepolyester product. Of course, it should be recognized that the targetlevel of cleaning or decontamination can depend upon the ultimate enduse of the polyester. In particular, the process is capable of providinga recycled polyester product having improved properties, e.g., a highdegree of cleanliness, good color and even an improved intrinsicviscosity. Moreover, the disclosed process is capable of providing theseproducts at an acceptable yield and at a lower processing cost since,e.g., it does not require “re-polymerization” of the monomers incontrast to typical depolymerization processes.

These and other modifications and variations to the present inventionmay be practiced by those of ordinary skill in the art, withoutdeparting from the spirit and scope of the present invention, which ismore particularly set forth in the appended claims. In addition, itshould be understood that aspects of the various embodiments may beinterchanged both in whole or in part. Furthermore, those of ordinaryskill in the art will appreciate that the foregoing description is byway of example only, and is not intended to limit the invention sofurther described in such appended claims.

1. A method for separating contaminants from polyester comprising:providing a mixture comprising contaminants and polyester; removing aportion of the contaminants from the mixture in an elutriationoperation, wherein contaminants heavier than the polyester are removedfrom the mixture during the elutriation operation; combining the mixturewith an alkaline composition; and saponifying only a portion of thepolyester according to a saponification reaction between the alkalinecomposition and the polyester.
 2. The method according to claim 1,wherein the alkaline composition is an aqueous composition, the mixturebeing combined with the alkaline composition to form a slurry.
 3. Themethod according to claim 2, further comprising mixing the slurry in ahigh energy mixer, wherein said mixing imparts sufficient energy to saidslurry so as to promote the saponification reaction between thepolyester and the alkaline composition and wherein the saponificationtakes place in the high energy mixer according to the saponificationreaction, wherein any heat added to the slurry in the high energy mixeris not sufficient to independently promote the saponification reactionof the polyester with the alkaline composition.
 4. The method accordingto claim 1, further comprising heating the mixture to a temperature thatis not greater than the melting point of the polyester in a heat settingoperation, wherein the mixture is heated in an environment includingless than about 80 ppm water content. 5-9. (canceled)
 10. A method forseparating contaminants from polyester comprising: providing a mixturecomprising contaminants and polyester wherein the contaminants comprisealuminum; combining the mixture with an alkaline composition in alow-energy mixer to form a slurry; reacting the alkaline compositionwith at least a portion of the aluminum while the mixture is in thelow-energy mixer; mixing the slurry in a high energy mixer, wherein saidhigh-energy mixing imparts sufficient energy to said slurry so as topromote a saponification reaction between the polyester and the alkalinecomposition; and saponifying only a portion of the polyester in thehigh-energy mixer according to the saponification reaction, wherein anyheat added to the slurry in the high-energy mixer is not sufficient toindependently promote the saponification reaction of the polyester withthe alkaline composition.
 11. The method according to claim 10, furthercomprising heating the mixture to a temperature that is not greater thanthe melting point of the polyester in a heat setting operation, whereinthe mixture is heated in an environment including less than about 80 ppmwater content.
 12. The method according to claim 10, the method furthercomprising rinsing the slurry following reaction of at least a portionof the aluminum and adding additional alkaline composition to the slurryprior to the saponification reaction in the high-energy mixer.
 13. Amethod for separating contaminants from polyester comprising: providinga mixture comprising contaminants and polyester, wherein thecontaminants comprise metal; removing at least a portion of the metalcontaminants from the mixture in at least one metal detection andremoval operation wherein the at least one metal detection and removaloperation comprises at least one bank of metal detectors, each bankcomprising two or more metal detectors in series combination, parallelcombination, or a combination of both; combining the mixture with analkaline composition; and saponifying only a portion of the polyesteraccording to a saponification reaction between the alkaline compositionand the polyester.
 14. The method according to claim 13, wherein thealkaline composition is an aqueous composition, the mixture beingcombined with the alkaline composition to form a slurry.
 15. The methodaccording to claim 14, further comprising mixing the slurry in a highenergy mixer, wherein said mixing imparts sufficient energy to saidslurry so as to promote the saponification reaction between thepolyester and the alkaline composition and wherein the saponificationtakes place in the high energy mixer according to the saponificationreaction, wherein any heat added to the slurry in the high energy mixeris not sufficient to independently promote the saponification reactionof the polyester with the alkaline composition.
 16. The method accordingto claim 13, further comprising heating the mixture to a temperaturethat is not greater than the melting point of the polyester
 17. Themethod according to claim 13, wherein the at least one metal detectionand removal operation comprises formation at each metal detector of anaccepted stream and a rejected stream, the method further comprisingrecycling at least one rejected stream through the metal detection andremoval operation.
 18. The method according to claim 13, wherein the atleast one bank of metal detectors comprises at least two metal detectorsin series, wherein the metal detectors in series exhibit increasingsensitivity to metal with progression of the series.
 19. The method ofclaim 1, wherein the elutriation operation includes a fluid flow rate ofbetween about 1.02 cfm per pound of mixture fed to the elutriationoperation per hour and about 1.84 cfm per pound of mixture fed to theelutriation operation per hour.
 20. (canceled)